Self-starting compact arc lamp



s p 5, 1970 (5. E. LIENHARD ETAL 3,529,209

SELF-STARTING COMPACT ARC LAMP Filed June 12, 1967 FIG. 2

INVEN TOR.

OTTO E. LIENHARD BY MICHAEL SKAL AGENT United States Patent 3,529,209SELF-STARTING COMPACT ARC LAMP Otto E. Lienhard, Upper Montclair, andMichael Skal, Passaic, N.J., assignors to Engelhard Hanovia, Inc.,Newark, N.J., a corporation of New Jersey Filed June 12, 1967, Ser. No.645,187 Int. Cl. H01j 7/36; Hb 31/22 US. Cl. 315--327 1 Claim ABSTRACTOF THE DISCLOSURE BACKGROUND OF THE INVENTION Compact arc lamps of thetype containing electrodes spaced apart less than about 1 cm. in anionizable atmosphere comprising rare gas, e.g. xenon, at a pressureabove about 2 atmospheres, e.g. 3-12 atmospheres, at temperatures ofabout 25 C. have been used as light sources of high intensity, e.g. insearchlights. Starting the arc of such lamps normally requires muchhigher voltages than the voltages necessary to operate the lamps. Thehigh voltage necessary to start such lamps is conveniently supplied bywell known pulse-type ignition circuits. To ignite a DC. xenon lamp,e.g. having an operating voltage of 22 volts, requires high voltagepulse of the order of 20 to 30 kv. and in addition, for the first secondof operation, a DC voltage of at least 70 volts. After ignition the lampmay be operated from a 24 volt battery. The high voltage starter and themeans to provide the initial elevated DC. voltage together weighapproximately 40 lbs. Another disadvantage of interest in the use of ahigh voltage pulse-type starter is the radio interference produced byit.

The present invention contemplates to eliminate to a large degree theabove-mentioned disadvantages by eliminating the necessity forhigh-voltage starting and the heretofore necessary high-voltage startingcircuitry.

SUMMARY OF THE INVENTION The invention deals with a low voltage startingcompact arc lamp herein regarded as a self-starting compact arc lampsince it does not require separate pulse-type high voltage nor boosterhigh voltage starting circuitry, the arc ignition being accomplished byDC. supply voltages of the order of about 16 volts to 36 voltsappropriately ballasted to provide lamp-operating voltages of from about15 volts to about 30 volts. The lamp comprises a tubular quartz envelopecontaining a pair of electrodes spaced apart from each other less thanabout 1 cm. and electrical input means hermetically passed through bothends of the envelope. One of the electrodes, preferably the cathodeelectrode, is movable relative to the anode electrode and is providedpreferably at one end portion thereof with a magnetic body, e.g., amagnetic body of ferromagnetic material at the end portion remote fromthe anode and operating as a solenoid core movable within a magneticfield provided by a pair of solenoid coils longitudinally adjacent oneanother and mounted coaxially of the lamp envelope on the outer surfaceof the lamp envelope. One of the coils provides a magnetic field to movethe cathode towards the anode and the other coil provides a magneticfield to move the cathode away from the anode. The core is provided atone end thereof with a conductor longitudinally flexible within the lampenvelope and connected to input leads appropriately hermetically sealedthrough the end of the lamp. Thus, when the lamp input terminals areconnected to a battery of approximately 24 volts in series with a properresistor to limit the operating current to the desired value, the lampis started without need of any high voltage RF starter or boostervoltage simply by moving the cathode through magnetic interaction withthe magnetic core towards the anode until the cathode and anode toucheach other and then magnetically retracting the cathode to its spacedoperating position immediately thereafter.

DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a partly cross-sectionaland partly elevational view of a lamp according to the invention, and

FIG. 2 illustrates an enlarged elevational side view of lamp componentsalong lines 2-2 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, theself-starting compact arc lamp of the invention comprises a tubularfused quartz envelope 1 having initially open opposite end portions 2and 3. An anode assembly is hermetically sealed into end portion 2. Theanode assembly comprises a molybdenum seal foil 4 having input leads 5welded to one end thereof and a tungsten anode electrode 6 mounted onone end of a stem 7 with the other end of the stem being welded to theopposite end of the seal foil 4. A short quartz collar 8 is mounted onstem 7 intermediate the seal foil 4 and anode. The anode assembly ispositioned into lamp end tube with the input leads 5 extending outwardlythereof, and the envelope is heat sealed onto the seal foil 4 and thecollar 8 whereby the anode assembly is hermetically sealed by means ofthe foil 4 and the quartz collar 8 contacts the inner tube wallsmaintaining the anode rigidly centered in the lamp envelope. Anelongated quartzbushing 9 having a precision bore 10 formedlongitudinally therethrough is mounted inside the envelope 1 and securedagainst the inner walls of the envelope substantially midwayintermediate the ends 2 and 3 of the envelope. A cathode assembly ishermetically sealed into end portion 3. The cathode assembly comprisesan elongated cathode electrode 11 having a length exceeding that of thebushing 9 and a diameter slidably fittable in precision bore 10 ofbushing 9. One end of the cathode is mounted on an end 12 of cylindricalcore 13 composed of ferromagnetic material. The other end 14 of the core13 is provided with a short stud 15 extending axially thereof and towhich is welded one end 16 of a flexible corrugated molybdenum conductorstrip 17. The other end 18 of the conductor strip is welded to one endof a molybdenum seal foil 19 with input leads 20 welded to the oppositeend of seal foil 19. The cathode assembly is positioned into the lampenvelope with the cathode 11 passing into close fitting slidableengagement with precision bore 10 of sleeve 9 and the input leadsextending outwardly of the end portion 3. A quartz sleeve 21 is passedinto the end portion 3 over the input leads 20, seal foil 19, andcorrugated conductor 17 with its outer surface engaging the inner wallsof the envelope and until its end 22 is spaced from the end 23 ofbushing 9 a greater distance than the length of cylindrical core 13, andwhereby the end 22 acts as a calculated motion-limiting abutment for thecore 13. Having so positioned the cathode assembly, both the lampenvelope and the quartz sleeve are partially fused at the area 24 overthe seal foil 19 to hermetically seal the lamp. With the lamp soassembled, it is apparent that the core 13 is movable longitudinally ofthe envelope -1 between the motion-limiting abutment 22 and the anode'6, which determine the arc gap, and consequently moves the tip 25 ofcathode 11 into and out of touching contact with anode 6 to provide anarc gap of about 0.080". In order to accomplish such movement while thelamp is energized without any deterrent physical resistance to motion,the molybdenum conductor 17 is rendered longitudinally flexible, i.e.expansible and contractable, by virtue not only of its corrugatednature, but because the conductor 17 is a composite conductor of aplurality of foil strips 26, 27 and 28 each about 0.003" thick bonded toeach other only at end portions 29 and 30 to provide both sufficientcurrent carrying mass while having a flexibility greater than if thelayers were completely bonded to each other. This construction enablesthe cathode movement with minimum force.

Having mounted the electrodes and hermetically sealed the lamp ashereinbefore described, the lamp is provided with an ionizableatmosphere of xenon at a pressure between about 3-12 atmospheres whencold, i.e. at a temperature of about 25 C., and a pair of solenoid coils31 and 32 are mounted on the lamp envelope. The pair of coils 31 and 32are mounted on the envelope adjacent one another longitudinally of andco-axially of the envelope with the core 13 positioned co-axially andsubstantially centrally intermediate the outer ends of the combined pairof coils. The coils are encased in an iron shell 31a and 32a andseparated from each other by a partition 31b. The coils 31 and 32 areeach independently energized as illustrated by FIG. 1 by a source ofvoltage, e.g. a 12-volt battery. Conductor leads 33 and 34 are connectedto coil 31 and conductor leads 35 and 36 are connected to coil 32. Whenthe lamp leads 5 and 20 are connected with a source of DC. voltage (notshown) the switch 37 is closed and switch 38 is opened whereby the coil31 is energized to magnetically move the core 13 which moves the cathodetip 25 into contact with anode 6. As

soon as the contact is made, the switch 37 is opened, and switch 38 isclosed whereby the coil 32 is energized to magnetically move the core 13to the position shown in FIG. 1 and cathode 11 is retracted to assume aspaced position of the cathode tip 25 relative to anode 6 establishingthe arc gap therebetween.

Consequently, by the structure hereinbefore described, the lamp iseasily self-ignited without the employment of high voltages.

Various modifications of the invention are herein contemplated withinthe scope of the appended claim.

We claim:

1. A high pressure arc lamp comprising a substantially tubularlight-transmissive envelope containing an anode electrode and a cathodeelectrode positioned to provide an arc therebetween and an ionizableatmosphere at a pressure above about two atmospheres at a temperature ofabout 25 0, one of the electrodes being movable relative to the otheraxially of the lamp envelope, said one electrode having a magnetic bodymounted thereon,

a bushing means having a bore formed therethrough coaxially of theenvelope and mounted in the lamp envelope, said one electrode beingslidably movable in the bore of said bushing,

said magnetic body is mounted on one end of said one .electrode remotefrom the other electrode, a sleeve coaxially mounted in the envelope inspaced relationship with said bushing and the magnetic body beingpositioned in the space between the bushing and the sleeve, saidmagnetic body being movable in said space axially of the envelope andabuttable withthe ends of said bushing and said sleeve, the degree ofmovement of said magnetic body in said space being a calculatedmotion-limiting movement determining the length of the arc gap betweenthe anode electrode and cathode electrode,

seal means at an end portion of said envelope, a flexible longitudinallyexpansible and contractable conductor strip secured to and between saidmagnetic body and said seal means,

said flexible conductor is composed of a plurality of corrugated foilstrips bonded to each other only at their end portions,

a pair of solenoid coils mounted on the lamp envelope adjacent oneanother longitudinally of andcoaxially of the envelope, electricalcircuit means for independently energizing each of the solenoid coils,the magnetic body being positioned coaxially centrally inter mediate theouter ends of the combined pair of the coils for response to themagnetic field of either solenoid coil when electrically energized, andmeans for selectively electrically energizing each coil to magneticallymove the magnetic body and consequently the said one electrode axiallyof the lamp envelope.

References Cited UNITED STATES PATENTS 287,067 10/1883 Tibbits 335-256 X2,446,855 8/1948 Seibel 335-256 745,427 12/1903 Edmonds 313-152 X758,842 5/1904 King 315-327 X 769,637 9/1904 Rice 315-327 X 902,427 10/1908 Mildebrath 315-327 X 1,344,757 6/1920 Darran 315-327 X 2,016,13110/1935 Beese 313-152 X 2,492,669 12/1949 Taylor 313-152 X 2,545,3453/1951 Deri 313-152 X 3,278,778 10/1966 Retzer 313-217 X JAMES W.LAWRENCE, Primary Examiner D. OREILLY, Assistant Examiner US. Cl. X.R.

